1. Field of the Invention
This invention relates to an improved process for producing a mixture containing cyclohexanol and cyclohexanone.
More particularly, the invention relates to an improved catalytic process for production of a mixture containing cyclohexanol and cyclohexanone wherein cyclohexane is oxidized in air to produce a reaction mixture containing cyclohexyl hydroperoxide (CHHP) and the cyclohexyl hydroperoxide is decomposed.
The principle products of the decomposition, cyclohexanone and cyclohexanol, are readily converted by oxidation to adipic acid. Adipic acid is used in large volume in the preparation of condensation polymers, particularly polyamides.
2. Description of the Prior Art
The oxidation of cyclohexane to mixtures containing cyclohexanes and cyclohexanol is a well-known, competitive, large-volume industrial process. The product is frequently referred to as K/A (Ketone-Alcohol) mixture. Experience in the operation of the process, which is reflected in the disclosures of many patents, has taught that the oxidation must be carried out at low conversion, if it is desired to maximize the yield of K and A and minimize the formation of other oxidation products, some of which have deleterious effects in the production of adipic acid and/or on the purity of the adipic acid produced. Relatively minor process improvements, such as in the yield of K and A, can result in highly beneficial cost advantage. There is, therefore, a strong economic incentive to increase the efficiency of the oxidation process.
U.S. Pat. No. 2,851,496 issued to Gates et al on Sept. 9, 1958 discloses a process comprising the oxidation of cyclohexane with molecular oxygen optionally in the presence of a catalyst to obtain a mixture containing cyclohexanol, cyclohexanone and cyclohexyl hydroperoxide and heating said mixture in the presence of a bed of solid peroxide decomposition catalyst to decompose the CHHP.
U.S. Pat. No. 3,530,185 issued to Pugi on Sept. 22, 1970 discloses a process for preparing partial oxidation products of cyclohexane which includes contacting at elevated temperature and pressure a stream of liquid cyclohexane at each of several successive stages of an oxidation zone with a mixture of gases including molecular oxygen at controlled partial pressure and inert gas. The patent discloses that a catalyst, such as a cobalt compound, can be present during the oxidation, and will cause cyclohexyl hydroperoxide formed during said oxidation to decompose.
U.S. Pat. No. 3,957,876 issued to Rapoport et al on May 18, 1976 discloses a process for oxidation of cyclohexane to produce a product fluid consisting essentially of unreacted cyclohexane, cyclohexanone, cyclohexanol and greater than 15% of cyclohexyl hydroperoxide by weight based on total products, consisting essentially of passing a fluid containing cyclohexane and a cyclohexane soluble cobalt salt, such as cobalt naphthenate, cobalt octoate, cobalt laurate, cobalt palmitate, cobalt stearate, cobalt linoleate or cobalt acetylacetonate, in the amount of 0.1 to 5 parts per million parts of product fluid through a series of oxidizing zones while contacting the fluid with a gas containing molecular oxygen.
U.S. Pat. No. 3,987,100 issued to Barnette et al on Oct. 19, 1976 discloses cyclohexane oxidation in the presence of a binary catalyst system comprising specific amounts of chromium and cobalt, reacting any cyclohexyl hydroperoxide that may be formed in the presence of said binary catalyst system, and recovering a product of cyclohexanone and cyclohexanol in a specified ratio.
An important step in the rather complicated overall oxidation process is the decomposition of cyclohexyl hydroperoxide (CHHP), which is a primary oxidation product of cyclohexane. See for example U.S. Pat. Nos. 2,851,496, 3,923,895, 3,925,316, and 3,927,105. Since the efficiency of this decomposition step contributes to the efficiency of the overall oxidation process, improvements in the decomposition of CHHP are a desirable objective.
Depending on process conditions, the decomposition of CHHP can take place in a number of ways.
CHHP can decompose "by itself," in which case all the cyclic C.sub.6 moieties in the K and/or A produced come directly from CHHP.
In the presence of cyclohexane, CHHP also decomposes by a reaction involving the cyclohexane, and some of the cyclohexane is converted to K and/or A. This mode of decomposition is discussed in U.S. Pat. No. 2,851,496 and is also referred to in U.S. Pat. Nos. 3,957,876 and 3,987,100. U.S. Pat. No. 2,851,496 represents this process as being the reaction of one mole of cyclohexane with one mole of CHHP to give two moles of A. In the present work, however, the reaction has been found to yield both K and A, as reported in U.S. Pat. No. 3,987,100. This involvement of cyclohexane in the production of K and A is referred to herein as "cyclohexane participation."
Cyclohexane participation results in a higher conversion of cyclohexane to useful oxidation products than would be realized if the CHHP decomposed by itself. It would be of great advantage to increase the amount of K and A derived from cyclohexane via cyclohexane participation without lowering the yield of K and A derived directly from CHHP.
Semenchenko et al, Russ. J. Phys. Chem. 47 (5), 654, (1973) have found that the decomposition of CHHP in cyclohexane in the presence of cobalt stearate is initially rapid and then slows down, i.e., the activity of the catalyst falls rapidly as the hydroperoxide decomposes.
Certain cobalt complexes with anionic heterocyclic nitrogen-donor ligands apparently catalyze the decomposition of other organic hydroperoxides. For example, Hock and Kropf, J. Prakt. Chem. 9, 173, (1959) tested the phthalocyanine derivatives of seven different metals as catalysts for the autoxidation of cumene (isopropylbenzene). They found that cobalt phthalocyanine gave the highest overall conversion of cumene to oxidation products, the highest conversion of cumene to K/A mixture, and the lowest conversion to cumene hydroperoxide in the final product mixture. Since the ketone and alcohol (acetophenone and 2-phenyl-2-propanol) are known to be decomposition products of the hydroperoxide, it can be inferred that the cobalt compound was the best catalyst for the decomposition of the hydroperoxide. The amount of hydroperoxide in the final product mixture was small but significant, and corresponded to 5.8% of the cumene originally charged.
Kamiya, Kogyo Kagaku Zasshi 72 (8), 1693, (1969); Chem. Abstr. 72, 11793Y, (1970) reports that cobalt phthalocyanine was a better catalyst than cobalt dodecanoate in the oxidation of cumene, and for the autoxidation of ethylbenzene. In each case the activity was "due to the decomposition of hydroperoxides."
Ochiai, Tetrahedron 20, 1819, (1964) studied the mechanisms by which transition metal stearates and transition metal phthalocyanines, including those of cobalt, participate in the autoxidation of cyclohexene. The author concluded that cobalt stearate decomposed the intermediate hdyroperoxide to form free radicals, and suggested that cobalt phthalocyanine was "liable" to decompose the hydroperoxide and undergo decomposition itself at the same time. The nature of the final products and the relative efficiencies of cobalt stearate and cobalt phthalocyanine are not reported.
In summary, improvements in the oxidation step and/or the decomposition step of the process for making from cyclohexane a mixture containing cyclohexanol and cyclohexanone are highly desirable objectives.